It is difficult to obtain accurate prevalence estimates of opiate addiction with direct methods.

The capturerecapture method has been used to estimate the prevalence of hidden populations, including opiate addicts.

In this study, we applied capture-recapture, including log-linear modeling, to estimate the prevalence of opiate addicts in Barcelona, Spain.

Anonymous identification data from three 1989 sources (hospital emergency rooms, treatment admissions, and heroin overdose deaths) in Barcelona were used to obtain population samples.

For prevalence estimation, two strategies were followed : 1) emergency room data only, divided into trimesters ; and 2) all three sources used simultaneously.

Estimates based only on emergency room data were lower than estimates obtained by the simultaneous analysis of all three data sources ; the latter estimates gave narrower confidence intervals (6,324-7,414 addicts), giving a prevalence for Barcelona in 1989 of between 8.5 and 9.9 opiate addicts per 1,000 residents aged 15-44 years.

The estimated prevalence varied by sex and age group and was highest in males aged 15-29 years (between 17.1 and 21.2).

At least 42% had contacted one or more of the services studied, although only one in seven had been admitted for treatment during 1989.

Capture-recapture is the election method for prevalence estimation when direct methods are not feasible.